During the fabrication of semiconductor wafers, undesirable oxide layers or other contaminants, i.e., hydrogen, carbides and other organics, may form on the semiconductor wafer surface. These contaminants adversely affect the reliability and performance of the wafers. The importance of cleaning semiconductors to ensure their basic efficacy is further discussed, for example, in U.S. Pat. No. 5,470,266, issued on Nov. 28, 1995 to Donald H. Stanley, Robert Peckman, and Weston K. Peregoy, Jr., entitled LOW TEMPERATURE PROCESS AND APPARATUS FOR CLEANING PHOTO-CATHODES. The Stanley U.S. Pat. No. 5,470,266 was assigned to ITT Corporation, a related company to the assignee herein, and is hereby incorporated by reference.
A wide variety of methods for cleaning semiconductor wafers have been developed. In the past, many of these methods have involved heating the semiconductor wafers within the reaction tube or vacuum chamber in which the wafers are fabricated. Increasing the temperature serves to break the bonds of the oxides and release the contaminants from the surface of the wafer. Commonly, however, cleaning of semiconductor wafers with the application of heat has been accomplished by placing the wafers on a heat source, such as a heater block, or next to a radiative source, such as a lamp, located inside the vacuum chamber in which the semiconductor wafers are fabricated. Shortcomings exist with regard to such methods. One shortcoming is that excess heat can be created within the vacuum chamber or reaction tube, which is undesirable as semiconductor materials are often strongly temperature dependent.
Another shortcoming of using an internal heat source is that, it is necessary to handle the wafers to position them onto the heater block or next to the lamp before cleaning. The step of handling the semiconductor wafer is disadvantageous in that it is time-consuming and poses a risk of handling damage.
A still further shortcoming with regard to the above cleaning methods is that they typically are not addressed to methods for cleaning a plurality of semiconductor wafers or photocathodes. Instead, the cleaning methods have been addressed to cleaning one semiconductor or photocathode at a time. Up until recently, there essentially has been no need to develop a bulk cleaning method, because the technology has been to activate and fabricate photocathodes individually, that is, one at a time. However, it recently has been discovered that a plurality of photocathodes can be simultaneously fabricated, thus reducing the time and increasing the efficiency of the production process. Such a method is disclosed, for example, in co-pending U.S. patent application Ser. No. 08/801,567, filed Feb. 18, 1997, entitled PROCESS OF ACTIVATING A PLURALITY OF PHOTOCATHODES, involving inventors Donald Stanley, Robert Peckman, Roger M. Voss, and Joseph H. Reich; this application also is assigned to ITT Manufacturing Enterprises, Inc., the assignee of this application, and is hereby incorporated by reference. Accordingly, there now is a need for a method of simultaneously cleaning a plurality of photocathodes or semiconductors.
Therefore, it is an object of the present invention to provide a method of cleaning semiconductor wafers that avoids heating the wafers with a heat source located inside the reaction chamber; that avoids the need to handle the wafers during the fabrication and/or cleaning process; and that can be used to simultaneously clean a plurality of semiconductor wafers. It is a further object of the present invention to provide a cleaning method that is simplified as compared with previous cleaning methods. Further objects, features, and advantages of the present invention will become more apparent to those skilled in the art as the nature of the invention is better understood from the accompanying drawings and detailed description.